Electrical discharge machining device using logical control

ABSTRACT

An automatic electrical discharge machining device, including a logic circuit and detecting units monitoring voltages and currents at different parts of the machining device circuit. The detecting units deliver their outputs to the logic circuit, for determining short circuit, large gap conductance, sustained arcing, and other detrimental conditions at the discharge gap, by suitably combining the outputs from the detecting units. Automatic control is made in response to the output from the logic circuit for regulating an electrode or various voltage pulses.

United States Patent Inventor Iwao Koudo 39-9 Kita-lnachi l-chome, Nerima-ku, Tokyo, Japan Appl. No. 9,566 Filed Feb. 9, 1950 Patented Jan. 4, 1972 Priorities Feb. 7, 1969 Japan 44/9554;

Feb. 7, 1969, Japan, No. 44/9555; June 11, 1969, Japan, No. 44/46422; June 11, 1969, Japan, No. 44/46423; June 11, 1969, Japan, No. 44/46424; July 24, 1969, Japan, No. 44/513503; Oct. 2, 1969, Japan, N0. 44/78754 ELECTRICAL DISCHARGE MACHINING DEVICE [56] References Cited UNITED STATES PATENTS 2,769,078 10/ 1956 Matulaitis 219/69 P 2,841,686 7/1958 Wi11iams.... 219/69 G 3,052.8 l 7 9/ 1962 Branker 219/69 C 3,056,065 9/ 1962 Porterfield 219/69 P X 3,161,752 12/1964 Stuart 219/69 G 3,264,517 8/1966 Ullman et a1. 219/69 P X 3,340,478 9/1967 Poerschke 219/69 G X 3,378,667 4/1968 Webb 219/69 P 3,390,246 6/1968 Webb 219/69 P 3,443,153 5/1969 Berghausen 219/69 C X Primary Examiner-R. F. Staubly Attamey-Waters, Roditi, Schwartz & Nissen ABSTRACT: An automatic electrical discharge machining device, including a logic circuit and detecting units monitoring voltages and currents at different parts of the machining device circuit. The detecting units deliver their outputs to the logic circuit, for determining short circuit, large gap conductance, sustained arcing, and other detrimental conditions at the discharge gap, by suitably combining the outputs from the detecting units. Automatic control is made in response to the output from the logic circuit for regulating an electrode or various voltage pulses.

mamwm 4m: 3 e32 942 SHEET OlUF 21 PATENIEI] JAN 4 SHEET 03 HF 21 PATENTEU JAN 4 I372 SHEET UL; 0F 21 PATENTEU JAN 4 I972 SHEET 05 HF 21 FIG.9

PIC-3.8

DTz

FIGJO CURRENT Pmmmm 4m 3.6321942 SHEET OBOF 21 D T2 DTs PATENTED JAN 41972 VOLTAGE 3,632,942 SHEET O'IUF 21 CURRENT FATENTEI] JAN 4 I872 SHEET UBUF 21 FIG.I5

DTI'

DTz

FIGJS g5 PATENTED JAN 4:972

SHEET 10UF 21 FIG.I9

Ill

PATENTED JAN 4 I972 SHEET 13 HF 21 PATENTED JAN 4 I972 SHEET 1 0F 21 FIG.28

PATENTED JAN 4 I972 SHEET IBM 21 PATENTED MN 41912 SHEET lBUF 21 FIG.29

Pmmmm 4m- 8.632.942

SHEET 18UF 21 FIG.3| 

1. Device for machining a conductive workpiece by means of intermittent discharge of relatively large electric power added to relatively small electric power for insulation breaking through to be applied across a gap between said workpiece and a movable electrode, comprising means for detecting high voltage and low voltage of said small power for break through and low output voltage and high output current of said large power for machining separately and independently in the discharge machining circuit, and logic circuit means for analyzing the detected values in combination to produce signals respectively representing normal machining condition, nondischarge condition, short-circuit condition and gap conductance condition to be utilized for controlling the machining automatically.
 2. Device as claimed in claim 1, including means for detecting gap conductance, and means responsive to detected conductance for withdrawing said electrode from the workpiece so as to eliminate said conductance.
 3. Device as claimed in claim 1, further comprising means for superimposing high-voltage pulses providing for insulation breakthrough on low-voltage pulses for machining in phase, said means being adapted to produce intermittently interrupted pulses to generate m pulses in every n successive actuating pulses, wherein n is a positive integer of at least 2 and m is a positive integer of (n -1) at the most, consist merely of said low-voltage pulses, and logic circuit means for subjecting to logic analysis the detected value of said intermittently lacking pulses together with said separately and independently detected values to produce a further signal representing undesirable sustained arcing condition to be utilized for controlling the machining more precisely.
 4. Device as claimed in claim 1, further comprising means for superimposing high-voltage pulses on low-voltage pulses out of phase, and logic circuit means for subjecting to logic analysis the detected value of said resulting pulses together with said separately and independently detected values to produce a further signal representing undesirable sustained arcing condition to be utilized for controlling the machining more precisely.
 5. Device as claimed in claim 4, further comprising means for narrowing the pulse width of the subsequent pulses applied across the gap in response to the detection of the undesirable arcing condition in respect of the preceding pulses.
 6. Device as claimed in claim 4, further comprising means for preventing at least each one of subsequently coming high- and low-voltage pulses from entering said superimposing means to form intermittently lacking pulses in response to the detection of the undesirable sustained arcing condition in respect of the preceding pulses.
 7. Device as claimed in claim 4, further comprising means for lowering the maximum current value of low-voltage electric pulses for machining in response to the detection of the undesirable sustained arcing condition in respect of the preceding pulses.
 8. Device as claimed in claim 1, further comprising means for counting the number of discharges per unit of time merely during the normal machining condition to be detected by said logic circuit means, means for determining an electrode feed during said unit time period, and means for subjecting to logic analysis the value of said determined electrode feed to produce a further signal of the value as a function of the effective area of the electrode to be utilized for controlling the machining more precisely.
 9. Device as claimed in claim 8, in which any of the maximum value of peak value current and the duty factor thereof is automatically determined depending on said electrode area function value. 